Numbers 32:28-32

So Moses gave the command regarding them to Eleazar the priest, to Joshua the son of Nun, and to the heads of the fathers’ households of the tribes of the sons of Israel.

And Moses said to them, “If the sons of Gad and the sons of Reuben, everyone who is armed for battle, cross with you over the Jordan in the presence of the Lord, and the land is subdued before you, then you shall give them the land of Gilead as their property;

but if they do not cross over with you armed, they shall instead be settled among you in the land of Canaan.”

And the sons of Gad and the sons of Reuben answered, saying, “As the Lord has said to your servants, so we will do.

We ourselves will cross over armed in the presence of the Lord into the land of Canaan, and the property of our inheritance shall remain with us across the Jordan.”